Specifically has to identify a problem, discuss its severity and effects, and then propose a researched solution.
What have you always wanted to learn more about?
What areas of your major are most interesting to you?
What problems exist in your field of study that will need solutions in the future?
What do you find controversial? What do most people think incorrectly about?
What do you think people need to change to find more health or happiness?
What community, national or global issues do you care about?